The present invention relates to a method of aluminizing a steel article while maintaining a relatively high yield strength and in particular it relates to products produced by such a method such as pump rods, tubing, valves, and other tools used in oil and gas wells where corrosive environments are encountered and where corrosion and high temperature resistance are desirable. The method of this invention can be practiced in conjunction with many tools which are made of carbon or low alloy steel that meet a prescribed chemical composition and special processing requirements described herein.
The various components of downhole production pumps and the rod string attached thereto must often operate under severe environmental conditions. Presently, carbon or low alloy steels used to make these downhole tools often fail prematurely when operating in a corrosive environment. This is very costly because of loss of production as well as the enormous expense of equipment and labor required to carry out such an operation. Moreover, the use of recognized corrosion resistant materials, such as stainless steels, nickel alloys, and other costlier materials, make drilling and producing a well extremely expensive, and many of these materials do not possess sufficient strength to operate in wells where high stresses are encountered.
Where a corrosive well requires the use of steel tools, and in order to maintain sufficient structural integrity of the tool, a corrosion inhibitor is often injected into the downhole fluid in an effort to provide a protection against corrosive environments. In many of these wells, however, higher bottomhole temperatures are encountered which render these chemical inhibitors ineffective. In order to overcome this drawback the downhole tools are sometime coated with nonmetallic coatings such as fused plastic. However, these types of protective coatings are also often rendered ineffective due to the high temperatures and abrasive well fluids. On the other hand, some metallic coatings, such as nickel or chromium alloys, suitably protect against these high temperatures and corrosive fluids. These coatings are made of expensive metals and applied either electrolytically or by spray coating using very high tempertures which significantly lowers the strength of the tools. Additionally these coatings are not diffused into the steel matrix, and therefore no interdiffusion reaction takes place between the base metal and the coating to provide a new intermetallic layer.
In view of these circumstances, it can be appreciated that it is desirable to produce tools which possess exceptional performance characteristics in corrosive environments at much reduced cost than is presently available.